The present invention relates to an eccentric orbiting type speed reducer for use with the industrial machine such as an industrial robot or machine tool, and a joint of the industrial machine equipped with the eccentric orbiting type speed reducer, and more particularly to an eccentric orbiting type speed reducer having a plurality of crankshafts in which a rotational force is applied to one of the plurality of crankshafts, and a joint of the industrial machine equipped with the eccentric orbiting type speed reducer.
Conventionally, the joint of the industrial machine equipped with the speed reducer is well-known in which a rotational driving force output from a servo motor is input into a plurality of crankshafts of the speed reducer via a gear supported with the rotational axis on the same straight line as the rotational axis of the speed reducer, as described in JP-A-7-108485, for example.
Referring now to FIGS. 10 and 11, a joint 800 of the industrial machine as described in JP-A-7-108485 will be described below.
If a rotational driving force is output from a servo motor 801, the rotational driving force output from the servo motor 801 is input via a gear 802 into the gears 806 and 807 supported by the bearings 804 and 805 so that the rotational axis may be on the same straight line as the rotational axis of a speed reducer 803. The rotational driving force input into the gears 806 and 807 is input via a plurality of gears 808, 809, 810 and 811 disposed to be mated with a gear 807 into a plurality of crankshafts 803a, 803b, 803c and 803d of the speed reducer 803.
In FIG. 10, though the details of the speed reducer 803 are not shown, the speed reducer 803 rotates a body of rotation 820 with respect to an anchor block 830 secured in the floor in accordance with a rotational driving force input into the plurality of crankshafts 803a, 803b, 803c and 803d, if the rotational driving force is input into the plurality of crankshafts 803a, 803b, 803c and 803d. 
As described above, the joint 800 of the industrial machine rotates the body of rotation 820 with respect to the anchor block 830 secured in the floor, if the rotational driving force output from the servo motor 801 is input into the plurality of crankshafts 803a, 803b, 803c and 803d of the speed reducer 803.
Also, another joint of the industrial machine equipped with the speed reducer is well-known in which a rotational driving force output from the servo motor is input into a specific crankshaft of the speed reducer, and the remaining crankshafts of the speed reducer via a gear disposed at the top end of the crankshaft having the rotational driving force input and a gear supported so that the rotational axis may be on the same straight line as the rotational axis of the speed reducer, as described in JP-A-9-57678, for example.
Referring now to FIGS. 12 and 13, a joint 900 of the industrial machine as described in JP-A-9-57678 will be described below.
If a rotational driving force is output from a servo motor 901, the rotational driving force output from the servo motor 901 is input via the gears 902 and 903 into a specific crankshaft 905 of a speed reducer 904, and input into the remaining crankshafts 910 of the speed reducer 904 via a gear 903 disposed at the top end of the crankshaft 905, a gear 908 supported by the bearings 906 and 907 so that the rotational axis maybe on the same straight line as the rotational axis of the speed reducer 904, and a gear 909.
The speed reducer 904 rotates the body of rotation 920 with respect to an anchor block 930 secured in the floor in accordance with a rotational driving force input into the crankshafts 905 and 910, if the rotational driving force is input into the crankshafts 905 and 910.
As above described, the joint 900 of the industrial machine rotates the body of rotation 920 with respect to the anchor block 930 secured in the floor, if a rotational driving force output from the servo motor 901 is input into the plurality of crankshafts 905 and 910 of the speed reducer 904.
Accordingly, in the joint of the conventional industrial machine, since the rotational driving force output from the servo motor is input in equal quantity into the plurality of crankshafts of the speed reducer, it is possible to prevent the life of the speed reducer, particularly, the life of the crankshafts from being shorter.
However, in the joint of the conventional industrial machine as described above, since a rotational driving force output from the servo motor was input in equal quantity into the plurality of crankshafts for the speed reducer, it was required to have a gear supported with the rotational axis on the same straight line as the rotational axis of the speed reducer, and a bearing for supporting the gear. Therefore, there was the problem that the manufacturing costs were increased due to the increased number of parts. That is, in the joint 800 of the industrial machine as shown in FIGS. 10 and 11, it is required to have the gears 806 and 807 supported so that the rotational axis may be on the same straight line as the rotational axis of the speed reducer 803, and the bearings 804 and 805 for supporting the gears 806 and 807. In the joint 900 of the industrial machine as shown in FIGS. 12 and 13, it is required to have the gear 908 supported so that the rotational axis may be on the same straight line as the rotational axis of the speed reducer 904, and the bearings 906 and 907 for supporting the gear 908.
It is an object of this invention to provide an eccentric orbiting type speed reducer that can be manufactured at low costs by preventing an increase in the number of parts, and a joint of the industrial machine equipped with the eccentric orbiting type speed reducer.
According to the present invention, there is provided an eccentric orbiting type speed reducer comprising an internal tooth member having the internal teeth formed on the inner circumference, a first rotational member with a plurality of circular grooves formed inside that is carried rotatably by the internal tooth member, while keeping a coaxial relation with the internal tooth member, a second rotational member with a plurality of circular grooves formed inside, the plurality of circular grooves being opposed respectively to the plurality of circular grooves for the first rotational member, the second rotational member being carried rotatably by the internal tooth member, while keeping a coaxial relation with the internal tooth member, an external gear having the external teeth formed on the outer circumference, with a plurality of through holes formed inside, the external teeth meshing with the internal teeth of the internal tooth member, the external gear being carried between the first rotational member and the second rotational member, a plurality of crankshafts having the first insertion portions to be inserted respectively into the plurality of pairs of opposed circular grooves for the first rotational member and the second rotational member, and the second insertion portions to be inserted respectively into the plurality of through holes for the external gear and orbiting eccentrically the external gear, a plurality of pairs of first bearings for holding the first insertion portions of the crankshafts rotatably with respect to the first rotational member and the second rotational member, respectively, and a plurality of second bearings for holding the second insertion portions of the crankshafts rotatably with respect to the external gear, characterized in that the basic radial load rating of the first bearing into which the first insertion portion of one of the plurality of crankshafts is inserted is greater than the basic radial load ratings of the first bearings into which the first insertion portions of the remaining crankshafts among the plurality of crankshafts are inserted. With this constitution, the eccentric orbiting type speed reducer of this invention can prevent the life of the first bearing for rotatably holding the crankshaft having the rotational driving force input from being shorter. Therefore, the rotational driving force may be input into one crankshaft alone among the plurality of crankshafts. Consequently, the eccentric orbiting type speed reducer can be manufactured at lower costs by preventing an increase in the number of parts. In the eccentric orbiting type speed reducer of the invention, the hardness of a rolling element of the first bearing for holding rotatably the crankshaft having the rotational driving force input is more than those of other first bearings. In this way, it is possible to prevent the life of the first bearing for holding rotatably the crankshaft having the rotational driving force input from being shorter, while the first bearing for holding rotatably the crankshaft having the rotational driving force input is identical in dimension to the other first bearings.
Also, according to the invention, there is provided an eccentric orbiting type speed reducer comprising an internal tooth member having the internal teeth formed on the inner circumference, a first rotational member with a plurality of circular grooves formed inside that is carried rotatably by the internal tooth member, while keeping a coaxial relation with the internal tooth member, a second rotational member with a plurality of circular grooves formed inside, the plurality of circular grooves being opposed respectively to the plurality of circular grooves for the first rotational member, the second rotational member being carried rotatably by the internal tooth member, while keeping a coaxial relation with the internal tooth member, an external gear having the external teeth formed on the outer circumference, with a plurality of through holes formed inside, the external teeth meshing with the internal teeth of the internal tooth member, the external gear being carried between the first rotational member and the second rotational member, a plurality of crankshafts having the first insertion portions to be inserted respectively into the plurality of pair of opposed circular grooves for the first rotational member and the second rotational member, and the second insertion portions to be inserted respectively into the plurality of through holes for the external gear and orbiting eccentrically the external gear, a plurality of pairs of first bearings for holding the first insertion portions of the crankshafts rotatably with respect to the first rotational member and the second rotational member, and a plurality of second bearings for holding the second insertion portions of the crankshafts rotatably with respect to the external gear, characterized in that the basic radial load rating of the second bearing into which the second insertion portion of one of the plurality of crankshafts is inserted is greater than the basic radial load ratings of the rolling elements of the second bearings into which the second insertion portions of the remaining crankshafts among the plurality of crankshafts are inserted. With this constitution, the eccentric orbiting type speed reducer of this invention allows the rotational driving force to be input into one crankshaft alone among the plurality of crankshafts. Consequently, the eccentric orbiting type speed reducer can be manufactured at lower costs by preventing an increase in the number of parts. Also, the eccentric orbiting type speed reducer of this invention can prevent the life of the second bearing for rotatably holding the crankshafts having the rotational driving force input from being shorter. In the eccentric orbiting type speed reducer of the invention, the hardness of a rolling element of the second bearing for holding rotatably the crankshaft having the rotational driving force input is more than those of other second bearings. In this way, it is possible to prevent the life of the second bearing for holding rotatably the crankshaft having the rotational driving force input from being shorter, while the second bearing for holding rotatably the crankshaft having the rotational driving force input is identical in dimension to the other second bearings.
According to the invention, there is provided a joint for an industrial machine comprising an eccentric orbiting type speed reducer for eccentrically orbiting an external tooth member with respect to an internal tooth member, and a motor having an output shaft for outputting a rotational driving force, wherein the eccentric orbiting type speed reducer comprises the internal tooth member having the internal teeth formed on the inner circumference, a first rotational member with a plurality of circular grooves formed inside that is carried rotatably by the internal tooth member, while keeping a coaxial relation with the internal tooth member, the second rotational member with a plurality of circular grooves formed inside, the plurality of circular grooves being opposed to the plurality of circular grooves for the first rotational member, the second rotational member being carried rotatably by the internal tooth member, while keeping a coaxial relation with the internal tooth member, an external gear having the external teeth formed on the outer circumference, with a plurality of through holes formed inside, the external teeth meshing with the internal teeth of the internal tooth member, the external gear being carried between the first rotational member and the second rotational member, a plurality of crankshafts having the first insertion portions to be inserted respectively into the plurality of pair of opposed circular grooves for the first rotational member and the second rotational member, and the second insertion portions to be inserted respectively into the plurality of through holes for the external gear, a plurality of pairs of first bearings for holding the first insertion portions of the crankshafts rotatably with respect to the first rotational member and the second rotational member, the first bearings being inserted into the plurality of pairs of opposed circular grooves for the first rotational member and the second rotational member, and a plurality of second bearings for holding the second insertion portions of the crankshafts rotatably with respect to the external gear, the second bearings being inserted into the plurality of through holes for the external gear, characterized in that the rotational driving force output from the output shaft is input into the crankshaft in which the basic radial load rating of the first bearing and/or second bearing is greater than those of the other crankshafts. With this constitution, the joint of the industrial machine of this invention allows the rotational driving force to be input into one crankshaft alone among the plurality of crankshafts. Consequently, the joint of the industrial machine can be manufactured at lower costs by preventing an increase in the number of parts. Also, the joint of the industrial machine of this invention can prevent the shorter life because of the use of the speed reducer with no shorter life.
The present disclosure relates to the subject matter contained in Japanese patent application No. 2000-141119 (filed on May 15, 2000), which is expressly incorporated herein by reference in its entirety.